The onset of whole-body regeneration in Botryllus schlosseri: morphological and molecular characterization

Colonial tunicates are the only chordates that regularly regenerate a fully functional whole body as part of their asexual life cycle, starting from specific epithelia and/or mesenchymal cells. In addition, in some species, whole-body regeneration (WBR) can also be triggered by extensive injuries, which deplete most of their tissues and organs and leave behind only small fragments of their body. In this study we characterized the onset of WBR in Botryllus schlosseri, one colonial tunicate long used as a laboratory model. We first analyzed the transcriptomic response to a WBR-triggering injury. Then, through morphological characterization, in vivo observations via time-lapse, vital dyes, and cell transplant assays, we started to reconstruct the dynamics of the cells triggering regeneration, highlighting an interplay between mesenchymal and epithelial cells. The dynamics described here suggest that WBR in B. schlosseri is initiated by extravascular tissue fragments derived from the injured individuals rather than particular populations of blood-borne cells, as has been described in closely related species. The morphological and molecular datasets here reported provide the background for future mechanistic studies of the WBR ontogenesis in B. schlosseri and allow to compare it with other regenerative processes occurring in other tunicate species and possibly independently evolved. Overall design: Transcriptomic profile of whole-body regeneration of Botryllus schlosseri at 0, 6, 18 and 24 hours post-injury

群居被囊动物（colonial tunicates）是唯一一类可在无性生命周期中，从特定上皮组织（epithelia）和/或间充质细胞（mesenchymal cells）起始再生，定期形成完全功能完整个体的脊索动物（chordates）。此外，部分物种的全身再生（whole-body regeneration, WBR）还可由大范围损伤触发——此类损伤会耗尽机体绝大多数组织与器官，仅残留少量身体碎片。本研究以长期作为实验室模型的施氏菊海鞘（Botryllus schlosseri，一种群居被囊动物）为研究对象，对其WBR的起始过程进行了系统表征。研究首先分析了WBR触发损伤后的转录组响应；随后通过形态学表征、活体延时观测（time-lapse）、活体染料（vital dyes）染色及细胞移植实验（cell transplant assays），重构了触发再生的细胞动态过程，阐明了间充质细胞与上皮细胞间的相互调控作用。本研究揭示的细胞动态过程表明，施氏菊海鞘的WBR起始于受损个体释放的血管外组织碎片，而非此前近缘物种研究中报道的特定血液源性细胞群。本研究报道的形态学与分子数据集，为未来开展施氏菊海鞘WBR个体发生（ontogenesis）机制的研究提供了核心理论基础，同时可用于与其他被囊动物物种中可能独立演化出的再生过程进行对比分析。整体实验设计：采集施氏菊海鞘在损伤后0、6、18及24小时的全身再生样本的转录组特征。